Transportable buildings such as mobile homes are typically built upon a frame containing two or more longitudinal members and several transverse beams. This frame serves as both a support for the flooring of the building, and as a mounting base for wheel axles and towing couplers while the building is being transported. Although the frame may be designed with considerable strength to endure the loads on the structure encountered while the building is in transit, the frame design usually lacks any provision for stable, secure placement of the building when a destination is reached.
Most commonly, a mobile hole is positioned on a site be towing the home into place, jacking it up off its wheels, and placing a number of piers under the frame. When the jacks are removed, the piers bear the weight of the mobile home, which sits elevated above the ground. Mobile home piers are generally pyramidal or conical in shape, and may be made of bricks, steel, or concrete. While the piers may have provisions for leveling the mobile home and equally distributing the weight among the set of piers, there is basically no secure attachment of the mobile home frame to the piers. Hence, only the weight of the mobile home, pressing down through the frame onto the piers, keeps the mobile home in place.
Under ordinary circumstances, a mobile home may rest on its piers with apparent security, because no lateral forces are present to displace the structure. However, significant lateral forces may arise from natural events such as severe windstorms, or more importantly, earthquakes. The lateral forces developed in an earthquake may cause the mobile home to shift off the piers and crash to the ground, injuring persons and property. The piers themselves may cause significant damage by piercing through the flooring of the building when the frame shifts laterally.